Conventionally, positioning devices for calculating a current position of a movable body itself based on signals from GPS (Global Positioning System) satellites are known. As a specific example of such positioning devices, a GPS navigation device to be attached to a vehicle body of an automobile can be given. Such a navigation device calculates a current position, etc., of the automobile based on signals from the GPS satellites, and displays information of the current position, etc., on a display screen.
With this kind of navigation device, in a situation where the signals from the GPS satellites cannot appropriately be received, such as a case where the automobile is traveling through a tunnel, positioning based on the signals from the GPS satellites cannot appropriately be performed. Thus, general navigation devices are configured to be able to calculate the current position without depending on the signals from the GPS satellites (so-called autonomous navigation).
To achieve the autonomous navigation in the navigation device, information of a moving velocity of the automobile needs to be acquired in some kind of manner. Thus, an acquisition of the information of the moving velocity of the automobile from a speed meter, etc., of the automobile can be considered. However, to acquire the information in the above manner, the vehicle body of the automobile and the navigation device need to be, for example, wired therebetween, which causes a disadvantage that attaching operation of an add-on/portable type navigation device to the vehicle body becomes complicated.
Thus, a configuration is proposed, in which components such as an acceleration sensor, etc., are built in the navigation device and an estimate of the moving velocity of the automobile is calculated based on the information of the sensors.
In this regard, Patent Document 1 discloses an equation VT=D/ΔT (Equation 1 in Patent Document 1) based on a perspective that a general relationship among time, distance and velocity can be established among a time difference ΔT between an acceleration of a vehicle in an orthogonal direction to a traveling surface and a pitch rate (pitch angular velocity) of the vehicle, a distance D from a mounted position of the navigation device to a position where the pitch angular velocity is assumed to cause effect, and a velocity VT of the vehicle. Upon the establishment of this equation, Patent Document 1 discloses a velocity calculating device for calculating the velocity VT based on the rate of the distance D with respect to the time difference ΔT. Thereby, Patent Document 1 concludes that a velocity of a movable body can accurately be calculated.